The HVEM has remarkable potential as an instrument which will allow a correlation of morphology with physiology and function. This potential has not been fully realized in the mammalian central nervous system, principally because the necessary techniques have not been systematically developed. This work will develop both specimen preparation and instrumentation needed to combine the power of both methods. Specimen preparation methods will be developed to localize sites on single mammalian CNS neurons at which neurologic, pharmacologic or toxic agents have been applied. These methods will identify a volume of tissue for detailed study by serial thick sections in the HVEM. The deposition of collodial gold or fluorescent markers by means of a microelectrode at the site under physiologic study will identify the volume of tissue during sectioning. Since 0.25 or 0.5 Mum sections will be used, the site under study will be encompassed within a limited number of serial sections. Nearby areas on the same or different neurons will be observed as controls. Instrumentation will be developed to provide elemental analysis and enhanced contrast imaging of unstained specimens. First, our X-ray detector will be used to analyze tissue in which high levels of Ca have been manipulated. Second, a simple electron energy loss spectrometer (EELS) will be used to improve detection. These methods if adequately developed, will allow a variety of types of investigation directed at critical questions related to morphology and function in the mammalian central nervous system, such as 1) Determination of sites of action of transmitter (i.e. soma vs dendrites) and induced local morphological changes on single central neurons. 2) Determination of site of generation of field on synaptic potentials on a single neuron, with correlation with synaptic inputs. 3) Determination of relation of postsynaptic interval membraneous specialization relative to synaptic inputs, and their ultrastructure. 4) Local effects induced by discrete actions of toxins. 5) The morphological characterization of areas of subcellular localization of elements, particularly metals such as Ca++, Zn++, and Al+++ in neuronal and pathological tissues.